Computer-assisted surgery (CAS) systems assist surgeons in different types of surgery like neurosurgery, total hip replacement (THR) and total knee replacement (TKR). Each of these surgeries presents numerous methods following different sequences of steps.
In THR, the patient can be positioned on his/her back or on his/her side during the surgery. Also, the surgeon can start either by working on the femoral head or on the acetabulum. Surgeons commonly start a THR by firstly working on the acetabulum, and thus by resurfacing the acetabulum to insert an acetabular cup implant. In the event that the cup is installed prior to the femoral implant being implanted, there are a few difficulties if the cup is not properly installed at the first try. If it isn't properly installed, the surgeon may remove the cup and reposition it, which can prove difficult without damaging the bone of the pelvis. Alternatively, the surgeon may compensate for the misalignment when installing the femoral implant. If the femoral and acetabular cup implants are misaligned, there are greater risks of dislocation of the femur, or impingement between the femoral implant neck and the acetabular cup or the pelvis.
When compared to the femoral implant, there is a greater range of possible positions/orientations associated with the implanting of an acetabular cup. It would be desirable to provide a method for selecting an orientation of the acetabular cup once the femoral implant is implanted, to lessen the risk of misalignment.